Potentiometer



06L 1962 J. G. RUCKELSHAUS 3,059,197

POTENTIOMETER (VARIABLE RESISTOR) Original Filed June 7. 1952 \NVENTOR JOHN G. RUCKELSHAUS Syd I QTC'ORNEYS United States Patent and this application July 17, 1959, Ser. No. 827,936

6 Claims. (Cl. 338143) This invention relates tov a potentiometer, and to a method of making the same. More particularly, it relates to a variable resistor unit in which the value or resistance is readily adjustable and in which the resistance element is a metallic film.

This is a division of my copending application, Serial No. 292,367 filed June 7, 1952, now US. Patent No. 2,917,814, dated December 22, 1959.

An object of this invention is to provide a simple, low cost potentiometer having infinite resolution, high stability and having a resistance element containing a metallic film.

One other object of this invention is to provide a multiturn potentiometer of infinite resolution which can be easily adjusted along the entire resistance path and having a metallic film as the resistance element.

Still another object of the invention is to provide a miniature, non-wire wound stable potentiometer.

An object of my invention is to provide a metal film resistance unit that is stable and has a lower temperature co-efiicient of resistance.

One further object of my invention is to provide a resistor comprising an insulating tube whose interior is coated with a metalliferous surface and has terminal conductors at the ends thereof.

Other objects and features of my invention will become apparent from the following detailed description, taken in connection with the accompanying drawings, in which the FIGURE is a detailed sectional view of a potentiometer forming a preferred embodiment of the invention.

In order to manufacture a resistor with high resistance values for use as film resisors of this type, the helix employed, as shown in the drawing may be made in the form of a thread cut on the inside wall 17 of the cylinder 14. After evaporation of a metal thereon the surface of the thread can be cut or reamed and the helix of resistance material will result. Instead of accurately evaporating the metal, metal can be deposited to a value lower than required, then, by connecting the unit across a Wheatstone bridge or similar apparatus, careful adjustment of the unit can be made by the amount of material cut or reamed off. This unit can then have lug or wire terminals attached to each end and sealed, or a shaft carrying a moving contact can be inserted so that the unit can be used as a potentiometer or rheostat. Said cylinder 14 is made of any dielectric material such as ceramic, glazed ceramic glass tube or other suitable material. The inner surface 27 has a thread 28 cut thereinto and a metal film 29 evaporated thereon as described in the above cited application. A shaft 30 is supported by an insulating bearing 31 and an insulating bearing 32, attached to cylinder 14 at the ends thereof. The shaft 30 has a groove 34 running its length. In said groove 34 is a movable contacting member 35 which engages the helix coating 29 of alloy evaporated on cylinder 14. As shaft 30 is turned by means of knurled member 30a fixed to one end of shaft 30 contact 35 follows the helix coating 29 and slides along groove 34. A flexible wire 36 connects contact 35 to spring contact terminal 16a through a metal tip on shaft 30. As shaft 30 is turned, a variable resistance is thus obtained between terminal 16a and lead 18.

The resistor is made by first threading the interior of 3,059,197 Patented Oct. 16, 1962 cylinder 14, and then undercutting as shown to the depth of the thread. The cylinder may then be glazed and fired, after which the undercuts are coated with platinum or other metal paste up to the thread ends. The cylinders are then fired and baked. Next the alloy is then evaporated onto the interior of the cylinder 14 making off the undercut with platinum so that the alloy film contacts platinum on first and last thread in the cylinder. The thread is cut or reamed to the desired resistance as shown, by a Wheatstone bridge or other suitable instrument. Once the desired ohmage has been obtained, the cups 31 and 32, carrying their respective lead wires, 18 and 18a are forced into the respective undercuts and solder applied to the platinum to seal the unit.

While a preferred embodiment of my invention has been illustrated and described, it is to be understood that modifications as to form, arrangements of parts and use of materials may be made without departing from the spirit and scope of the invention as claimed herein.

I claim:

1. A variable resistor comprising an insulated tube, having metallic terminals fired onto each end, a helix of metallic film evaporatively deposited to a uniform thickness on the inner wall of said tube and forming inverse apices of the helix therein and overlying said terminals, a slider contacting said metallic film, and means for adjusting said resistor by moving said slider from one end of the film to the other along the entire resistance path thereby obtaining infinite resolution of resistance change when said slider is so moved and means of connecting at least one end of the resistance element.

2. A variable resistor comprising an insulating tube, metallic terminal bands fired on the ends of said tube and interfused therewith, a metallic film in the form of a helix deposited on the inner wall of the tube and extending from one terminal band to the other and overlaying at least a portion of each band, said film forming inverse apices of the helix therein, a shaft extending from one end of the tube to the other, means for supporting said shaft axially within said tube, sliding contact means on said tube, terminal means for said sliding contact, and means effective upon rotation of the shaft to cause the sliding contact to move angularly along the length of the helix, so that resistance between either end terminal and the sliding terminal may be varied as the shaft is rotated.

3. A resistor according to claim 2 wherein the tube is selected from the group consisting of glass, ceramic, and glazed ceramic.

4. A resistor according to claim 2 where the change in resistance is infinite in resolution as the sliding contact is moved along the path of the helix.

5. A resistor according to claim 2 wherein the ends of said resistor are sealed.

6. A resistor according to claim 2 wherein the inner wall of said tube is in the form of a thread said metallic film being deposited on said thread and comprising an alloy of nickel and chromium.

References Cited in the file of this patent UNITED STATES PATENTS 1,739,256 Pender et al. Dec. 10, 1929 2,371,159 Erb Mar. 13, 1945 2,547,405 Mitchell et al. Apr. 3, 1951 2,586,752 Weber et al. Feb. 19, 1952 2,792,620 Kohring May 21, 1957 2,860,221 Kohl Nov. 11, 1958 FOREIGN PATENTS 611,250 Great Britain Oct. 27, 1948 

